Effect of Ligand Modification on Rhodium-Catalyzed Homogeneous Hydroformylation in Supercritical Carbon Dioxide

Several fluoroalkyl- and fluoroalkoxy-substituted tertiary arylphosphines were synthesized and investigated in the homogeneous catalytic hydroformylation of 1-octene using HRh(CO)L 3 (L = tertiary arylphosphine). The activity of the rhodium complex (formed in situ from Rh(CO) 2 (acac) and L) increased with decreasing basicity of the phosphine according to the series [3,5-(CF 3 ) 2 C 6 H 3 ] 3 P > [4-CF 3 C 6 H 4 ] 3 P ≈ [3-CF 3 C 6 H 4 ] 3 P > [4-CF 3 OC 6 H 4 ] 3 P > [4-F(CF 2 ) 4 (CH 2 ) 3 C 6 H 4 ] 3 P. The very weakly basic phosphine (C 6 F 5 ) 3 P did not complex with Rh(CO) 2 (acac), most likely due to a combination of electronic and steric factors. Steric effects did not play a role in either the activity or selectivity of the rhodium catalysts that were formed under hydroformylation conditions.